First, decide which call option suits your needs:

If your speech isn't clear but you want to use your own voice or a voice output device

Speak and Listen calls are for people who can use their own voice or output device, but may be hard to understand on the phone. These calls allow you to speak and listen directly to the other person and use an ordinary phone.

If you can't speak but can type and hear

Type and Listen calls allow you to type what you want to say on a TTY and listen to the other person.

If you can't speak but can type and have access to the internet

Internet relay calls allow you to type what you want to say and read the messages from the other person on your computer or on some mobile phones.

If you can't speak but can type

Type and Read calls using a TTY allow you to type what you want to say and read the messages from the other person.